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Stresses of Thermal Loads

By John Hizer, P.E., S.E. / June 27, 2017

A thermal load is defined as the temperature that causes the effect on buildings and structures, such as outdoor air temperature, solar radiation, underground temperature, indoor air temperature and the heat source equipment inside the building.

ASCE 7-15 section 2.3.5 and 2.4.4 specifically mention thermal and other self-straining loads are to be considered, where applicable. For many cases, thermal movements cannot be restrained and instead designs need to allow for the structure/equipment to move thermally otherwise stresses in either the restraints or in the structure/equipment may cause catastrophic failures.
Different materials have different expansion rates. Structures or items with different types of materials connected by fasteners or adhesives can warp and break at extreme temperatures. For example, PE pipe will expand/contract around ten times more than steel pipe.

Historically, thermal stresses have caused failures in railroad tracks, roads and building facades and even electronic devices. Understanding these effects, and how to minimize them, reduces the risk of damage or failure at extreme temperatures and prevents having to perform costly repairs.

For example, a 200 ft long PE pipe can change in length by 1/8 of an inch per degree (F) of temperature change. If this movement is restrained, stresses in the pipe and the restraints will be generated. Depending on the strength of the restraint and the buckling strength of the pipe, the restraint could fracture or the pipe could buckle. Buckling pipes can injure anyone working next to the pipe and could also cause leaking of the pipe. Damage and injury could also occur when a restraint breaks.

Even sidewalks are not immune from thermal stresses. Recently a large section of 4’ wide sidewalk was installed about a block long. Thermal expansion joints were not provided at adequate spacing. During a hot summer day, a loud explosion was heard throughout the neighborhood. The sidewalk had buckled and one of the sections of sidewalk had shattered. The concrete was left uneven and damaged requiring removal and repair of the damaged area of the sidewalk. Additional thermal expansion joints were provided to hopefully prevent future problems.

Tags: Blog construction Existing Buildings Resources thermal loads Uncategorized

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